Processes for preparation of pectins are well known, as are many uses for these products. In general, typical pectin processes include the steps of:
(1) acid extraction from plant starting material at low pH, PA1 (2) purification of the liquid extract, and PA1 (3) isolation of the extracted pectin from the liquid.
In the acid extraction step, plant material is typically treated with dilute acids such as nitric-, sulfuric-, hydrochloric- or other inorganic or organic acids to remove the pectin from the cellulose components of the material. Commonly used plant starting materials are citrus peels from juice production and apple pomace from apple juice and cider production. Other plant starting materials can also be used, such as sugar beet, before or after sugar extraction, sunflower heads after removal of the seed, and other vegetables or waste products from plants. Extraction conditions are selected such that a major part of the pectin molecules contained in the plant starting material is transferred from the cell walls of said plant starting material to the extraction medium
The quantity and quality of the extracted pectin depends on the raw material source and the selection and control of the extraction conditions such as pH, temperature and extraction time.
ASfter the acid extraction step, a mixture of solid plant material and liquid that contains the pectin remains. This mixture is then subjected to a purification step in which the solid plant material is removed by filtration, centrifugation or other conventional separation steps known to those skilled in the art.
The extract can, optionally, be further purified by ion exchange and concentrated by evaporation of part of the water. Alternatively, the purification steps can be carried out by reverse osmosis, concentrating and purifying the extract in the same steps.
The pectin in the acid extract can be isolated by reacting with aluminum salts after adjusting the pH. The aluminum pectin gel thus formed is treated with alcohol/acid mixture to wash out the aluminum salt and transform the pectin into pectic acid. The pectic acid can then be neutralized and dried by washing with slightly alkaline alcohol.
More commonly, the pectin is isolated by treating the pectin solution with an appropriate alcohol to render the pectin insoluble in the ensuing blend of alcohol and water. Any alcohol or other organic solvent miscible with water can be used, most often ethyl alcohol, methyl alcohol or isopropyl alcohol, isopropyl alcohol is most preferred.
The insolubilized pectin is separated from the alcohol/water mixture by appropriate means such as filtration, centrifugation, etc. The resulting pectin cake is dried and milled to the desired particle size.
In typical commercial processes, the presence of high levels of polyvalent cation is avoided in steps (1) and (2) as described above. While low levels of cation, i.e., those levels naturally present in the starting material, may be tolerated in some instances. It has been the general practice to never add additional cation(s) to the processes. This would result in unacceptable increases in viscosity and unacceptable levels of insoluble pectin in the final product.
Industrially produced pectins are made up primarily of anhydrogalacturonic acid chains in which rhamnose may be found. Neutral sugars may be attached to the rhamnose units. The anhydrogalacturonic acid makes up at least 65% of the dry matter in commercial type pectins. The galacturonic acids are partly esterified with methyl alcohol.
According to convention, pectins with more than 50% of the carboxylic acids groups esterified with methyl alcohol are referred to as high methoxyl pectins; whereas, pectins with less than 50% of the carboxylic acid groups esterified with methyl alcohol are called low methoxyl pectins.
The extract as obtained by the commercial production is composed of those molecules that are soluble under the conditions of pH, temperature, and time used during the extraction. The extract is composed of a mixture of molecules which differ according to molecular weight, distribution of molecular weight, and degree of esterification.
The properties of the pectin obtained are, therefore, very much dependent of the specific mixture of molecular configurations present in the isolated pectin. This mixture of molecules can be controlled only to a certain degree by the pectin manufacturer by selection of raw materials and extraction conditions. For this reasons, variation in pectin properties is seen from extract to extract, from manufacturer to manufacturer, and normalization of the properties is generally necessary. This may be accomplished by blending different extracts and diluting with acceptable diluent such as sugar, dextrose, fructose, etc.
One of the main functional variations between high methoxyl pectins is their sensitivity to the presence of varying concentrations of polyvalent cations. It is known that pectins of high degree of esterification, e.g., greater than fifty, are not particularly useful for applications involving reaction of the pectin with polyvalent cations such as calcium.
European patent application 0432,835 describes the production of a cation salt of pectin in the form of microgels. In said patent, a solution of pectin is reacted with a solution of a di- or trivalent metal salt, preferably calcium salts, under high shear conditions to create calcium pectin microgels with a mean equivalent diameter not exceeding 100 micrometers, more preferably not exceeding 50 micrometers. These microgels are described as being used as fat substitutes among other things.
U.S. Pat. No. 4,911,945 discloses a fat substitute of carbohydrate particles that display a fat-like mouthteel characteristic when the particles have a substantially spheroidal shape and a mean diameter distribution in the range of 0.1 about 2 microns with less than about 2% of the total particles being over 3 microns. The carbohydrates includes starches, gums, and cellulose and can be reacted with a calcium ion to form micro-colloid particles of the invention.
The above discussed references are seen to express a strong preference for the use of small particles for the successful simulation of fat in foods.